In the solution ring opening polymerization of cycloolefins, the product discharged from the reactor is a honey-like cement that consists principally of a nonpolar solvent in which the polymer is dissolved. The polymer content in the cement is normally on the order of about 15% by weight. The polymer can be any of the family of polymers that are made by polymerizing one or more of cycloolefins that contain the norbornene group.
After the honey-like cement is obtained, it is necessary to separate the polymer from the nonpolar solvent. This is accomplished by mixing in a high shear mixer about three volumes of a nonsolvent to about one volume of cement whereby the polymer precipitates out. A nonsolvent is a liquid that is miscible with the nonpolar solvent, however, the polymer is insoluble in the nonsolvent. Examples of suitable nonsolvents include methanol, ethanol, n-propanol, isopropanol, etc.
When polymer cement is mixed with a nonsolvent, the polymer coagulates or precipitates out of the solvent-nonsolvent liquid medium whereas the oligomers, catalyst residues, and other by-products and impurities remain solubilized therein. Thus, the precipitation procedure also performs the function of purifying the polymer. Polymer recovery in this manner, however, produces large volumes of contaminated liquid composed primarily of a nonsolvent, nonpolar solvent, and by-products and impurities. Solvent recovery from the large volumes of solvent-nonsolvent liquid is difficult and expensive, and is especially complicated when water extraction is employed and when water-free nonsolvents are used that form azeotropes with water.
Prior to precipitation of the polymer from cement, however, the cement can be preconcentrated from about 15% solids to 20 to 35% solids and above. Like precipitation, preconcentration is accomplished with a nonsolvent and the only critical difference being the amount of nonsolvent used. Whereas in precipitation about 2 to 6 volumes of nonsolvent is used to 1 volume of cement, in preconcentration, about 5 to 100 parts of nonsolvent is used per 100 parts of cement, on volume basis. Generally speaking, the amount of nonsolvent should be sufficient to preconcentrate but insufficient to precipitate the polymer. In preconcentration, the nonsolvent extracts a substantial portion of the solvent and impurities from the cement causing formation of a gel-like substance of increased viscosity having a higher polymer content.
U.S. patent application Ser. No. 376,368 entitled "Anhydrous Precipitation of Polycycloolefins" was filed May 10, 1982 for inventors Lane, Tenney and Wootton, now U.S. Pat. No. 4,400,501 issued Aug. 23, 1983. That patent is directed to precipitation of polycycloolefins from cements containing the polymer dissolved in cyclohexane solvent by the use of methanol as the nonsolvent. The precipitation approach disclosed in that application is based on the fact that, when boiled, cyclohexane and methanol form an azeotrope which separates into two phases on condensation, the upper phase being essentially cyclohexane and the lower phase being rich in methanol.